According to the developments in optical measurement techniques in recent years, detection and/or measurement of faint light at a single photon or single fluorescent molecule level have become possible by using an optical system of a confocal microscope and a super high sensitive light detection technique capable of the photon counting (single photon detection). Thus, there are variously proposed optical analysis techniques of performing detection of a characteristic, an intermolecular interaction, a binding or dissociating reaction of a biological molecule, etc. by means of such a faint light measurement technique. As such optical analysis techniques, for examples, there are known Fluorescence Correlation Spectroscopy (FCS, see e.g. patent documents 1-3 and non-patent documents 1-3), Fluorescence Intensity Distribution Analysis (FIDA, e.g. patent document 4, non-patent document 4) and Photon Counting Histogram (PCH, e.g. patent document 5). In addition, in patent documents 6-8, there are proposed methods of detecting fluorescent substances based on a time progress of fluorescence signals of a sample solution measured using the optical system of a confocal microscope.
Furthermore, in patent documents 9-12, Applicant of the present application has proposed a novel optical analysis technique, using an optical system which is capable of detecting the light from a micro region in a solution, such as an optical system of a confocal microscope or a multiphoton microscope, and employing a different principle from optical analysis techniques, such as FCS and FIDA. In the case of the novel optical analysis technique (Hereinafter, referred to as “Scanning Molecule Counting Method”.), the position of a micro area which is a detected region of light in a sample solution (Hereinafter, referred to as a “light detection region”. When excitation light is used, it almost coincides the condensing region of the excitation light.) is moved, i.e., the inside of the sample solution is scanned with the light detection region, and when the light detection region encompasses a light-emitting particle being dispersed and moving at random in the sample solution, the light emitted from the light-emitting particle is individually detected, and thereby each of the light-emitting particles in the sample solution is detected individually so that it becomes possible to perform the counting of the light-emitting particles and the acquisition of the information about the concentration or number density of the light-emitting particles in the sample solution.